The Door of Life" or Kidney Centre

Ming Men

Secondary (Yang) Chakra (rear)

The Ming Men ("Door of Life") centre is located between the second and third lumbar vertebrae,
just beneath the two kidneys, and opposite the navel, and approximately where the Muladharta is said to be externally located.

But once we study the symbolism we see a lot of discrepancies, and only a few similarities. In Tantric teaching, the Manipura is said to have ten petals, and corresponds to the element of fire. On the other hand, in Taoism, the Kidneys are associated with the element Water. Such contradictions
are common in comparisons of different spiritual teachings. My understanding
is that the Shakta Tantrics are referring to the Inner or primary Muladhara Centre, which pertains to a level of the Causal or Inner Being, while the Taoists are describing the outer or rear (secondary) Muladhara centre, here referred to as the Kidney Centre

As regards colour, Tantric writings variously describe the petals
as black, dark blue, or dark green in colour, while the central part of
the chakra is uniformly described as having a red triangle (symbolising
the tattva or element of fire). In Taoism, the Kidneys - that is,
the Kidney chakras, not the actual physical organs - are said to be black
or dark blue in colour. Again, two different subtle organs would
seem to be being described here.

The Ming Men ("Door of Life") is located just beneath the two
kidneys, and exactly opposite the navel. It is associated with the
element water and the trigramkan

This centre supports the kidneys, which not only purify the blood
but also store sexual and energetic essences and stimulate the body's chi
when it is low. It is called the Door of Life (Ming Men) because
it is the centre of Prenatal Chi or innate life-force. This centre
also serves as the "negative" or yin chi pole, in relation to the Heart
centre, which constitutes the "positive" or yang chi pole. These
two centres regulate the flow of chi in the body. [Chia, pp.241-2]

In Taoism, this is a very important centre, for it serves as the junction
with the Belt Channel, which encircles the body horizontally, and is activated
during higher stages of Taoist practice.

In the Chinese system, the Kidneys are associated
with the element Water and the planet Mercury.
In any case, the Qabalistic correspondence here would be the lower part
of the Sefirah Hod (traditionally associated with Mercury,
which I equate with the inner Manipura, a primary chakra).